1. Field of the Invention
This invention relates to a porous ceramic structure, which is suitable for use as a gas permeable heat insulator to be fitted in an exhaust port of a furnace or the like for the purpose of enhancing the heat efficiency of the furnace.
2. Description of the Prior Art
It has been known in the art to thermally insulate an exhaust port of a furnace or the like by means of a gas permeable heat insulator such as a fine ceramic honeycomb or a porous ceramic body having three-dimensional interconnected open cells, thereby shielding the furnace from radiation cooling and collecting the heat energy of exhaust gases by heat exchange as the gases pass through the gas permeable heat insulator. The collected heat energy is recycled directly by radiating the same toward the heating side as radiation heat (Japanese Patent Application Laid-Open No. 57-209892).
The conventional gas permeable heat insulators, including the above-mentioned ceramic honeycomb and porous ceramic body having three-dimensional interconnected open cells, exhibit excellent properties as long as they are used under conditions free of large temperature variations and dust. However, the ceramic honeycomb is liable to cracks or similar damages in the corner or edge portions when used under conditions with great changes in temperature. On the other hand, the porous ceramic body with its three-dimensional interconnected open cells is easily blocked when a large amount of dust (e.g., ashes generated in a combustion system or scales from heated material) is present in exhaust gases, resulting in an increase in pressure loss which is inviting trouble to the operation of the furnace.